* Carbon (C)

* Hydrogen (H)

* Oxygen (O)

* Nitrogen (N)

* Sulfur (S)

While the first four elements are common in many biological molecules, nitrogen is the key element that distinguishes amino acids. It is found in the amino group (-NH2) that gives amino acids their name. Sulfur is found in some, but not all, amino acids (specifically cysteine and methionine).